Thread cutting device



Oct. 26, 1937. F. JUDGE THREAIDQ CUTTING nnvxcs Filed Sept. 25, 1935 3Sheets-Sheet 2 .4 no tend n y for the 15001 to back p show the positionsof the teeth on each of these Patented Oct. 26, 1937 UNlTED smrss PATENToFHcE THREAD CUTTING DEVICE Franklin Judge, Greenfield, Mass, assignorto Greenfield Tap andDie Corporation, a corporation of MassachusettsApplication September 25, 1935, Serial No. 41,99f1 12 Claims. (Cl.10111) This invention relates to screw thread cutting Fig. 2 is a sideView in section, taken at line tools and has for its principal objectsto facilitate 2-2 of Fig. 1; starting of the tool and to ease thecutting opera Fig. 3 is a perspective view of one of the lands tionafter starting. of the die shown in Figs. 1 and 2;

6 Ordinarily, thread cutting tools such as dies Figs. 4, 5, 6 and 7 areenlarged partial views comprise anumber of lands provided with cuttingof the four lands, respectively, on the die of teeth thereon in helicalcontinuation. To assist Fig. l;

in starting in such cases as hand threading with- Figs. 8 to 19,inclusive, illustrate the cuts made out the aid of a lead screw themouth of the tool by each of the successive initial teeth of the 10: isusually chamfered, that is, some of the initial four lands; 10 teeth arepartially removed on a taper. Ordi- Fig.20 is a cross-section through acut thread n-arily the taper starts from a diameter slightly showing thecutting contributions of successive beyond the root of the thread at theface of the teeth; I tool and ends at the crest of some thread, usuallyFigs. 21, 23, 25, and 27 illustrate starting teeth the third or fourthfrom the beginning. differing in shape from those of Figs. 4 to 7; 5

When such chamfering is used, the tops of the and chamfered teeth of thetool increase in width Figs. 22, 24, 26 and 28 each show a crosstowardthe face; and these Wide surfaces offer section of a cut toothindicating the cutting conconsiderable resistance in starting thethreading ,tributions of the teeth of Figs. 21, 23, 25 and 27,operation. respectively. ,go It has been proposed to overcome thisstarting The pipe thread die of Figs. 1 and 2 comprises resistance bysplitting the wide chamfered teeth a solid base It! having the usualcenter opening ll into more threads per inch than the regu ar throughwhich the work to be threaded may prothreads of the tool, or bythreading the chamfered trude. Four lands I, 2, 3 and 4, integral withthe teeth deeper than the standard depth. Such base and extendingradially toward the center 25 starting devices have the disadvantage ofleavof the opening, are each provided with thread ing material on thework to be threaded, which .cutting teeth in a manner presently to bedeincreases the load on the remaining full teeth. scribed.

This is especially true when threading pipe with Pipe thread teeth l2are formed on each of 30 taper threads. the lands in helicalcontinuation. A chamfer is ,30

To overcome these objections the thread cutformed on a taper on thefirst three teeth adjacent ting tool of this invention is provided, withfine the leading face l3 of the die, thereby removing or small teethprotruding from the wide flat snrthe crests of these teeth and formingflat surfaces faces of the chamfer and having the ame pitch or shoulders[4. In accordance with this invenas, a registering W the regular threadsof tion a tooth is formed on the flat shoulder of each the tool. Thesefine or small teeth operate to take chamfered tooth. Fig, 3, which is anenlarged hold of the work to be threaded, regardless of perspective viewof land I shows the formation whether it has a burr. They serve also toremove f the small teeth [5, l9 and, 23, each on n of most 0f thematerial in the path of the fOllowing the chamfered full teeth, Thesestarting teeth full teeth, thereby lightening the load on the full ha ethe same number of threads per inch as 5 teeth. the regular full sizeteeth, and their crests are FlirtherIn re Since the material remOVed y espiral continuations of those on the full teeth. small or fine teeth islocated symmetrically in the Figs 4 t 7 re enlarged side vie of the pathof the following fullteeth there is little or t th d portions of lands lto 4, respectively, and r on the wor being threaded- Wh u a ki lands. Inthese figures the light line 21" shows up or creeping occurs imperfectthreads are apt the line of the full tooth crests of the tapered toform. pipe die. Line b shows the parallel to the The invention will bebetter unde from axis of the teeth, which coincides with the axis thefollowing detailed description of p p thread of the work on which thethreads are to be cut. 5 cutting i s and the accompanying r w of Thelight line 0 indicates the taper of the which: chamfer. The light lines01 show the positions Fig. 1 i a a w of a p ad di av the chamfered teethwould occupy if they were four an provided with teeth embodying thisunchamfered. The vertical tooth center lines invent e show that thecrests of the small teeth are 3 l to cutting threads are reached, thestarting teeth from l-to 26, inclusive; Tooth ETon land is the firstfull tooth.

are numbered consecutively l he first starting. tooth of land I isadjacent the leading face 13, and at each of the succeeding lands 2, 3and 4' the first starting tooth is located progressively further fromthe face, in conformity with the spiral of the tooth. It is noted thattheinverted V formed by the root 23 of the chamfered full teethbecomeswcrkQ Tooth the starting thread crest of the fullrtooth, as shown at thethird progressively'larger in. passing back from face 53, from. one landto the next until the V of almost coincides with the starting tooth in,Fig. 7. r V 7 Figs. 8 to 19, inclusive, illustrate the cuttingpositions, on each succeeding position of the first isnct shown in thisis located quite far outside the outer diameter of the work, and, if itshould strike anything, would only strike a largeburr. Tooth l6 of land2 is shown in 8 not quitein contact withjthe ll of land 3 is shown inFig. 9 to be making the first cut in the material; it is removing asmall V-shaped chip'or ribbon 29. The following tooth 18 on land 4 isshown retooth IE to 21, inclusive. The starting tooth [5 of land I'moving'a chevronefl centered 'onthe V 29 of tively.- The first full thecut thread is left by 'is the second starting tooth Fig. 9. The positionof the V29 isshowncin dotted lines to indicate how much material isremoved by. tooth l8.

Flg.;ll shows the material removed by the next succeeding tooth which I9of land I. In addition to the chevron 3| there is removed a wedge-shapedchip 32 by the shoulder 32d of the chainiered tooth on which the smalltooth I9 is built. The material removed by each of the next succeedingstarting teeth is indicated by to 39in Figs.'12 to 18, respecthenumerals 33 tooth 2Tmakes the cut In each of Figs. 8 to 19 the conditionin which the preceding tooth. light lines in Figs. 8

40' shown'in Fig. 1 9. the dotted ine indicates The large V '4! shown into 18 indicates the out which will finally be made by the first fulltooth 21.

Fig. 20 is a compositesectional view showing the cut made by each of theteeth up to tooth 21'. This figure clearly indicates the cutting con- 1j tributions of the shoulders and root portions of the'chamfered teeth.The side. cuts due to the forward and rear faces of the successivechamfered teeth are shown'exaggerated for the pur-' poseof'illustration, Actually, the sides of'the cut 'will'be shaved by thesuccessive chamfered' teeth, but not to the extent shown in Fig. 20. Thenumerals in the figure correspond'to those fin Figs. 9 to-lQ;

' It is observed that the successive initial teeth and also thefollowing full teeth cut thin chips or slivers. which are symmetricalwith respect to the preceding cutj thecrests of all the starting teethand of the following full teeth are aligned :at the cut thread.Inconsequence the initial teeth, including the chamfered. parts, leavevery' little material'in the path of the full teeth, so

that. the load on the full teeth is considerably, reduced. Furthermore,the substantially -sym-'- metrical character 'of the'suc'cessive cutsprac- Itically removes any tenden'cy for the die to back 7 up or creepwhile cutting. Backing Iup .01

'in Figs; 22, 24, 26 and the work W being threaded, of I group offigures because it materialto be threaded.

. oblique line g creeping is caused by the tendency of a cutting toothto'center itself in the cut; so if a tooth" were'cutting away morematerial on one side than on the other, it would tend to creep or back aup in the direction which would equalize the cut onthe two sides of thetooth. Such creeping or backing up, if it occurred, would injure the cutthread. a r

Figs. 21, 23, 25 and 27 show possible "modi fications of the startingteeth, and Figs. 22, 24, 26 and 28 are composite sectional views,similar to Fig. 20, showing the developments of the cut 3 thread made bythe teeth of Figs. 21, 23, 25 and 27, respectively. The slight sidecuts, or shav ings, made by the successive teeth are not obvious 28;'such cuts, or shav- ,ings, will actually occur in the manner shown inex'aggerated'form in Fig. 20; t r In. Fig. 21' the starting teeth,instead of being fine teeth, are coarse obtuse teeth 42, 43and M,

which extend entirely across the chamfer of the chamfered teeth on whichthey: are built. Fig;

22 shows that the symmetrical character of the walls make agreater'angle with the vertical than the rear walls.

41 of Fig. 23 are Another possible variation is shown in,:Fig.' 27 Vwherein the apices of the starting teeth are .lo-

catedaheadof the vertical line through the apex of the full cut thread.The apices of these starting teeth occur along an that is, the pitch, ornumber of teeth per inch, is slightly greaterthan that of the 'full'followingv teeth. This type of tooth removes more material atits rearwall'than at its forward wallso that the tendency is for the tool tocreep forward; This tendency would compensate for any opposite tendencywhich might existin some cases at the following full teeth.

Although the invention has been described with particular'reference todies it should be, understood that it is also applicable to taps. Hence'the'invention is notlimitedto dies, but only'by j the scope; of theappended claims. I claimzd 1. A thread cutting' tool comprisingplurality of, lands each of which is provided with thread cutting teeth,a. plurality of said teeth adjacent the leading face of said tool'havinga tapered chamfer, and'small starting'teethbuilt on the chamferedportions of said chamferedtee't'h, the

crests of 'said startingiteeth being on a taper which recedes from thecrests of the full cutting T "teeth, the relation of said startingteethto said" chamfered teeth beingcsuch that;the cut made 7 by all of saidstarting and chamfered teeth nearly coincides with the path of .afollowing full cutting tooth;

I 2.. A thread cutting tool/comprising a plurality of lands each ofwhich is provided with thread cutting teeth, a plurality of said teethadjacent the leading face of said tool havinga tapered chamfer providingshoulders which. become broader toward said leading face, and a smallstarting tooth built on at least some of said shoulders in such aposition that the cut made by all of said starting and chamfered teethvery nearly equals, and is substantially symmetrical with respect to,the path of the first full cutting tooth, the crests of said startingteeth being on a taper which recedes from the crests of the full cuttingteeth.

3. A thread cutting tool according to claim 2 in which the startingteeth are substantially V-shaped.

4. A thread cutting tool according to claim 2 in which the startingteeth are narrower than their associated chamfered shoulders so that aflat shoulder portion of a chamfered tooth extends on each side of thestarting tooth built thereon.

5. A thread cutting tool according to claim 2 in which the startingteeth extend the full width of the chamfered portions of the associatedchamfered teeth.

6. A thread cutting tool according to claim 2 in which each of saidstarting teeth has a rear wall which is more nearly vertical than theforward wall thereof.

7. A thread cutting tool according to claim 2 in which each of saidstarting teeth has a vertical rear wall and an oblique forward wall.

8. A die comprising cutting teeth for cutting an outside thread, saiddie having a chamfer providing flat teeth near its leading face, andsmall teeth located on said flat teeth, said small teeth having the samepitch as said cutting teeth and having crests which increase in diametertowards said face.

9. A thread cutting tool comprising cutting teeth the first few of whichare chamfered to provide flat teeth and relatively small teeth formed onthe chamfered teeth and having crests which taper away from the crestsof the unchamfered cutting teeth, said small teeth having the same pitchas, and registering with, said cutting teeth whereby the cuts made bysaid small teeth lie substantially symmetrically in the path of thefollowing cutting teeth.

10. A die comprising a leading face and a plurality of lands extendingperpendicular to said face, said lands having cutting teeth thereonarranged in helical continuation, saidteeth being chamfered at said faceso that'several consecutive teeth near said face are flattened, saidflattened teeth being provided with relatively small teeth having thesame number of teeth per inch and registering with said cutting teeth,the crests of said small teeth lying on a taper which is approximatelyparallel to the taper of the chamfer.

11. A die comprising cutting teeth and having a. chamfer on some of theteeth adjacent the leading face of said die and small starting teethbuilt on said chamfered teeth, said starting teeth being all ofsubstantially the same size and being substantially centrally locatedon, and having the same number of threads per inch as, said chamferedteeth, whereby said chamfered and starting teeth remove nearly all thematerial in the path of the following non-chamfered teeth.

12. A die comprising full cutting teeth and chamfered teeth near theleading face of said die, each of said chamfered teeth havingsubstantially symmetrically built thereon a small starting tooth, saidstarting teeth having crests which increase in diameter toward said faceand having the same number of threads per inch as, and being aligned inthe cut thread with, the following full teeth, whereby said full teethare not required to remove more than a small amount of additionalmaterial.

FRANKLIN JUDGE.

